Many types of speaker diaphragms are well-known in the prior art and are used to transduce electric vibration into mechanical vibration. A cone type diaphragm directs acoustic sounds toward fixed orientations like a horn while the cone itself vibrates depending on the sounds.
A cone is an essential and principal element in a speaker and has to have low frequency response characteristics and high flexusal wave propagation velocity.
Such a cone should also have high stiffness and light weight and should resist heat and humidity.
In the prior art, paper is commonly used as a speaker diaphragm material by forming the cellulose fibers of paper to a certain configuration using a mold.
However, the process for making the cone is usually complex and expensive.
Furthermore, as the stiffness and tensile strength of the paper is not so high, the thickness of the cone should be increased in proportion to the output power level of the speaker of the audio system which uses the cone (e.g. from 3 mm to 4 mm for a power level of 400 watt.). In addition, if the thickness is increased, the flexural wave propagation velocity and frequency response characteristics of the cone are seriously impaired and thus accoustic properties (especially low frequency response) are decreased.
Another disadvantage of paper as a cone material is its sensitivity to humidity and to heat, causing cones made of such material to eventually deteriorate.
Therefore, such a cone loses its vibration characteristics.
It is also known to produce such a cone by molding plastic material such as liquid crystal polymer, epoxy and etc.
However, such material is expensive and in some cases toxic and have poorer low frequency response characteristics.
The plastic material is highly sensitive to heat and readily deformed at an temperature over room temperature, inevitable resulting in acoustic distortion.
Especially, if the speaker having such a cone is mounted into an vehicle, it should be kept in mind the fact that the temperature inside the vehicle often violently rises, for example, upto 60.degree. C. or 70.degree. C.
In this circumstance, thermal deformation of the speaker cone is accelerated and the cone may even be ruptured due to the fluctuation of the temperature.
It will be understood that conventional speakers could not have desirable properties such as low frequency response and high flexural wave propagation velocity because of the problems concerning the material of the cone.